The present disclosure relates to modified polycationic polymeric materials and methods of modifying polycationic polymeric materials such as modified polyethylenimines having possible uses in gene or drug delivery, flocculating agents, or membranes, amongst others.
Polyethylenimines (also sometimes referred to as poly(ethylenimine), poly(iminoethylene), polyaziridine, and poly[imino(1,2-ethanediyl)]) are polycationic polymeric materials which, among many other uses, have been investigated as transfection agents in gene therapy applications. That is, polyethylenimines have been investigated as a possible delivery vehicle for genetic material payloads (e.g., DNA and RNA) to be incorporated (transfected) into targeted cells for therapeutic purposes. Other possible uses of polyethylenimines are found in detergents, adhesives, water treatment, and paper making.
Polycationic polymers in general, and polyethylenimines in particular, have been widely studied as polymeric gene delivery vehicles for use in gene therapy applications. That is, these polycationic materials have been investigated as means for protecting genetic material payloads (e.g., DNA and RNA) from enzymatic degradation and the like during transport through the body to targeted cells or tissue. Polyethylenimines are known to form polyplexes or polycondensates with genetic material due to electrostatic interactions between the amine groups of the polyethylenimine and phosphate groups in the nucleic acids making up the genetic material. Furthermore, materials with a polycationic character are considered to promote intake of the genetic material payload by target cells by promoting binding of polyplexes to the generally negatively charged cellular membrane. Once bound to the cellular membrane, the polyplex can pass into the interior of the cell by endocytosis. Once inside the cell, it still remains necessary for the genetic material to be released from the endosome into the cytoplasm and then reach the transcription mechanism inside the cell nucleus. Polyethylenimines provide a mechanism (the “proton sponge effect”) for rupturing the endosome and releasing the polyplex into the cytoplasm. Likewise the electrostatic nature of the binding between the polyethylenimine and the genetic material provides a means for releasing the genetic material into the cytoplasm for eventual diffusion into the nucleus. However, polyethylenimines are, in general, considered highly cytotoxic and, depending on molecular weight, may also be bioaccumulative. Since typical polyethylenimines are not readily biodegradable, in vivo accumulation is potentially problematic, especially given the known cytotoxicity.
Furthermore, polyethylenimines, and polycationic gene delivery vehicles more broadly, are known to cause problems when the overall positive charging of the polyplex relative to complexed genetic material is increased. In general, polycationic-genetic material complexes are more easily incorporated into cellular targets than bare genetic material because the polycationic material shields/mitigates the inherent negative charges of the genetic material, which would otherwise cause the genetic material to be repulsed by the cellular membrane. The binding of the polyplex to the cellular membrane is generally improved with increased positive charge, and thus ultimately uptake of the polyplex by a target cell is improved by increasing positive charging of the polyplex. However, polyplexes with substantial overall positive charge may themselves require shielding while within the various transport pathways of the body. For example, without shielding the polyplexes may trigger unintended immune system responses and interactions with blood components (e.g., plasma proteins), which might cause premature removal of the polyplex and/or dangerous aggregation of components within the blood stream or tissue. In some instances, a polyplex core of a delivery vehicle may in turn be shielded using materials like polyethylene glycol (PEG) or polyacrylic acid. However, providing additional shielding for the polyplex in this manner will tend to reduce effectiveness with respect to target cell binding and the genetic payload's bioavailability once inside the target cell. As such, existing polymeric gene therapy delivery vehicles face issues regarding cytotoxicity, transfection efficiency, bioaccumulation, and/or unintended interactions during transport to cellular targets. Therefore, development of improved materials for polymeric gene delivery vehicles for gene therapy applications is desirable.